1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of monosaccharides. More specifically, the invention relates to a process for separating arabinose from a mixture comprising arabinose and one or more additional aldoses, which process employs an adsorbent comprising a crystalline aluminosilicate, X-type faujasite to selectively adsorb arabinose from the feed mixture.
2. Description of the Prior Art
It is known that zeolites can be used to separate specific monosaccharides or classes of monosaccharides from carbohydrate feed mixtures. A specific example of a class separation is given in U.S. Pat. No. 4,024,331 disclosing the separation of ketoses from a mixture of ketoses and aldoses using a type X zeolite. Specific ketoses such as fructose can be separated from a feed mixture containing the same by an adsorptive separation process using an X or Y zeolite exchanged with selected cations at the exchangeable cation sites as disclosed in U.S. Pat. No. 4,340,724 to Neuzil et al. In the case of the X zeolite, barium, sodium and strontium ions are set forth. The Y-zeolite may be exchanged with ammonium, sodium, potassium, calcium, strontium, barium and combinations.
This invention is particularly concerned with the separation of arabinose from other monosaccharides. Obtaining pure arabinose has commercial significance in light of its potential as a starting material for the production of L-glucose, a possible nonnutritive sweetener. A common source of arabinose is the hydrolysis of hemicellulose in making pulp from wood or as a product of the conversion of plant tissue to sugars in biomass operations. Regardless of the source, L-arabinose is typically found in a mixture of many monosaccharides. Therefore, it is highly desirable to have a simple method for separating arabinose from the other monosaccharides present in the source mixture. However, in light of the ultimate food use of arabinose, the separation process must not provide contaminants that will render the arabinose or subsequent products unsuitable for human consumption.
Specific methods for separating arabinose are known in the art. U.S. Pat. No. 3,160,624 discloses the separation of D(L)-arabinose from D(L)-ribose by chromatography using a cellulose powder or ion exchanged resin. However, it is well known in the art that heretofore resin or cellulose adsorbents posed significant operational problems when their use is attempted on a large scale due to the high pressure drops associated with their use. However, newly developed methods of forming the ion exchange resins into very uniform spheres, as in U.S. Pat. No. 4,444,961 referred to hereinafter, reduce this tendency to cause high pressure drops. The zeolite adsorbents which are commonly used in large scale adsorptive separation processes have also been applied to the separation of arabinose from other mixtures of monosaccharides.
U.S. Pat. No. 4,516,566, is directed to the separation of L-arabinose from a mixture of sugar that exists in the hydrolysates of wood and beet pulp using water as the desorbent, with an X-type zeolite exchanged with barium cations.
Additional data related to potential adsorbents for a two-stage separation of arabinose from other monosaccharides is set forth in U.S. Pat. No. 4,471,114 insofar as it is pertinent, at column 7, lines 31-34. The passage just referred to relates to the use of a barium-exchanged Y-type faujasite. Due to the toxic properties of barium, this separation process will be difficult to apply when attempting to obtain food grade arabinose. It is also stated that NH.sub.4 -X zeolite is not suited to the separation of mannose from other monoscaccharides (column 7, lines 40-44).
A calcium-exchanged ion exchange resin (Dowex 50-W-X8) has been reported to separate arabinose from xylose sugars. P. Jandera et al., I. of Chromatography, 98 (1974) 55-104, p. 81.
In contradistinction to these findings, it has been discovered that X-type faujasites containing ammonium ions at cation exchanged sites are suitable adsorbents for the separation of arabinose from other monosaccharide aldoses. Moreover, the use of these zeolites with ammonium cations allows the purification of arabinose in a process that is acceptable for the food industry.